Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Strength
MDATA_FITCIRCLE_WEIGHT
Parameter: Roundness
MDATA_FITCIRCLE_ROUNDNESS
Parameter: Exact Radius
MDATA_FITCIRCLE_ABSOLUTERADIUS
Parameter: Scale
MDATA_FITCIRCLE_SCALE
Parameter: Radius
MDATA_FITCIRCLE_RADIUS
Parameter: Angle
MDATA_FITCIRCLE_ANGLE
Parameter: Adjust Inner Points
MDATA_FITCIRCLE_ADJUSTINNERPOINTS
Parameter: Project To Surface
MDATA_FITCIRCLE_PROJECTTOSURFACE
Parameter: Equal Spacing
MDATA_FITCIRCLE_PROJECTREGULAR
Parameter: Select Outline
MDATA_FITCIRCLE_SELECTOUTLINE